The handling and the performance of a motor vehicle is, to a considerable extent, a function of its current geometric inclination, i.e., if it is on a flat or an inclined roadway. For example, the control of the control systems mostly available in modern motor vehicles, such as ABS (anti-lock brake system), TCS (traction control system) and ESP (electronic stability program) should be adjusted to the specific vehicle inclination. These systems are equipped with acceleration sensors and speed sensors, and, in certain driving situations, they intervene in the brake management and engine management. Knowledge of the vehicle inclination is important for optimally controlling the braking performance and traction performance. Knowledge of the vehicle inclination may also have an influence on or be transmitted to the transmission control system, in order to improve the gear-shifting operations and protect against unintentional switching operations while driving uphill and downhill. In addition, the inclination of a stationary vehicle is also of interest, e.g., for protecting against rolling back unintentionally and optimizing the driveaway characteristics. Furthermore, knowledge of a transverse inclination, i.e., transverse to the driving direction, is very important for preventing a possible overturning hazard, especially in the case of so-called off-road vehicles, when the roadway conditions are difficult on pathless terrain.
In the case of conventional systems having special inclination sensors, it has turned out to be a problem that they often register incorrect inclination values in the event of simultaneous vehicle accelerations. Other systems only determine the values after a certain driving time or driving distance or are only suitable for determining longitudinal inclinations.
A method for detecting uphill or downhill driving of a motor vehicle is described in German Published Patent Application No. 100 26 102. The object of the method is to bring a reference speed, which is determined from wheel-speed sensor signals and can significantly deviate from the actual vehicle speed in certain situations, e.g., in the case of spinning wheels, toward the actual speed as rapidly as possible, in order to thereby improve the control of electronic systems, which refer to the reference speed. A reference acceleration is determined from the reference speed of the vehicle, using differentiation. This is compared to a sensor-determined, longitudinal vehicle acceleration. If the difference of the longitudinal vehicle acceleration and the reference acceleration exceeds a specified threshold value over a certain minimum period of time, then uphill or downhill driving is detected.
In the conventional method, it turns out to be disadvantageous that it only functions in the case of a moving vehicle, and that a certain distance traveled or driving time is necessary for detecting a vehicle inclination. In addition, it is only suitable for detecting longitudinal inclinations, i.e., inclines or declines, but not for detecting transverse inclinations. It is also disadvantageous that, in the case of all-wheel drive vehicles, the drive or transmission must be temporarily interrupted at one axle, in order to implement the method. In addition, a relatively complicated, digital, logical counting circuit is necessary.
A method for determining the longitudinal roadway inclination, one a motor vehicle is driven without braking it, is described in German Published Patent Application No. 43 08 128. In this connection, a slip difference is determined by comparing the wheel speeds of the wheels on a driven axle and a freely revolving axle. A flat roadway, an incline, or a decline is detected as a function of the combination of the slip-difference sign and the sign of a vehicle speed change determined from the wheel speeds.
In the case of the conventional method, it is disadvantageous that it is only usable while driving without braking. In addition, it is not designed for all-wheel-drive vehicles and is only suitable for determining a longitudinal inclination.
Therefore, an aspect of the present invention is to provide a method for determining a vehicle inclination, which may immediately provide the current geometric vehicle inclination, both during vehicle operation and when the vehicle is stationary, which may be suitable for determining longitudinal and transverse inclinations, and which may not require much effort to implement.